II 



bast and the cortex, with its suberous tissue, or bark. Careful 

 physiological investigations have shown that the ascending move- 

 ment of the salts and water of the soil takes place chiefly in the 

 wood, while on the other hand, the descending movement of the 

 iflorganic substances towards the roots takes place chiefly in the 

 bast, and possibly also in the cortex. Only in the case of a very 

 few plants does the pith participate largely in this transport, namely 

 in the case of those trees, where the pith contains a so-called 

 inner bast. 



It has been my experience that in all tissues suitable for 

 sap-transport, the descent takes place chiefly, and quickest, 

 in a straight direction parallel to the axis of the tree. 

 It appears that those rows of cells take the chief part in the 

 transport which run in an upward verticle direction in the stem,, 

 and the cells of which inter-communicate. If the organic 

 substances are forced to descend in an oblique instead of a 

 straight direction, the progress of sap circulation will become 

 markedly slower. 



But the parts of the stem not only perform the function of 

 channels for the constructive substances, they also form excellent 

 reservoirs for the temporary storage of those organic constructive 

 substances, which cannot be utilized at once, and which have beea 

 produced in excess. It is also of great importance to know, that 

 not only the channels which most rapidly transport the organic 

 substances, namely the bast and the cortex, form such reservoirs, 

 but so do all other parts of the stem, including the pith and the 

 wood, with its medullary rays, as long as they contain living cells. 

 The large; quantity of carbohydrates, particularly starch, which in 

 many trees is found in the living cells of the pith and wood are 

 nothing else but stored reserve material. As soon as they are 

 required, they can be conveyed from the reservoirs and used for 

 the growth of the stem or of other -parts of the tree. The 

 reservoirs, at least those contained in the wood, are filled from 

 the leaves by means of the normal channels which exist in the 

 trcv for the transport of organic substances: namely the bast and 

 the cortex. The most important subsidiary channels arc the 

 medullary rays, which penetrate deep into the wood. They also 

 transport the reserve material from the wood back again into 

 the chief channels. 



It is easy to see how highly advantageous it is for the \iulity 



